Picture-transmission system



Feb. 21, 1928.

E. P. BANCROFT ET AL PICTURE TRANSMISSION SYSTEM Filed Jan.l7. 1925 6 Sheets-Sheet 1 6 Sheets-Sheet 2 E. P. BANCROFT ET AL PICTURE TRANSMISSION SYSTEM Filed Jan.l'7. 1925 Feb. 21, 1928.

Feb. 21, 1928.

E. P. BANCROFT ET AL PICTURE TRANSMISSION SYSTEM 6 Sheebs-Sheec 3 Filed Jan 1925 NWN QWN Feb. 21, 1928. 1,659,716

E. P. BANCROFT ET AL PICTURE TRANSMISSION SYSTEM Filed Jan.l7. 1925 6 Sheets-Sheet 4 f7, i I m .7 4 g 30/ igg T 52a Va? TELEPHDNE INTERRUPTER Feb. 21, 1928. 1,659,716

E. P. BANCROFT ET AL PICTURE TRANSMISSION SYSTEM Filed Jan.l'7. 1925 6 Sheets-Sheet 6 PM; Feb. 21,1928.

UNITED STATES PATENT OFFICE.

ERWIN P. BAN CROFT AND J'OHN C. BURKHOLDER, JR, OF BROOKLYN, NEW YORK, AND

WALTER A. PHELPS, OF ATHENIA, NEW

JERSEY ASSIGNORS TO WESTERN ELEG- TBIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF miw YORK.

PICTURE-TRANSMISSION SYSTEM.

Application med January This invention relates to picturatransmission systems and more especially it has to do with an intercommunicating system for use with-such systems. '6 Ex erience with the transmission of pictures y electricity has proven that their transmission can be materially facilitated and expedited by the'use of some method of intercommunication between the transmitting and-receiving stations to inform the respec tive operators when everything is in readiness for the transmission of the picture and to permit the communication of other information necessary to the eflicient transmission of the pictures. Of course, the most practical way to accomplish this feature is through the use of telephonic means which has been used heretofore but which required the assignment of a separate and independent circuit between the connected points,

thereby considerably increasing the costof transmitting the pictures.

The principal object ofthlsinventlon 1s the accomplishment of signaling or tele-' phonic communication or bothover the same circuit as the picture currents.

According to the embodiment herein described, the present invention provides for intercommunication between stations connected for the transmission of pictures by electricity, by arranging apparatus which responds to the closure of a designated key for impressing on the connecting circuit a current frequency effective at a distant station for operating an indicating device. Telephonic communication may be carried on between the connected stations by operating appropriate keys at the respective stations which not only connects the telephone 40 instruments with the telephone circuit, but which also disconnects the transmitting and receiving picture apparatus, thereby preventing interference from this apparatus.

This invention is in the nature of an improvement on the system shown and described in a copending application to Horton et 211., Serial No. 714,466, file-d May 19, 1924, issued as Patent No. 1,606,227, Nov. 9, 1926, and a general reference is hereby made to that application for an understanding of the manner in which the mechanisms of the present system are arranged, and the details 17, 1925. Serial N0. 3,003.

are hereinafter mentioned but not particularly illustrated or described.

The term light as used herein includes not only radiations within the visible spectrum, but also radiations having wave lengths above and below those of the visible spectrum.

It is to be understood that the terms used hereln'in reference to picture transmission, both in the specification and claims, do not limit this invention to the producton of a picture record at the receiver from a picture record at the transmitter. The invention is equally applicable to systems, for example, 1n which a transitory image of a still or moving picture or object is produced at the receiver, as in certain forms of television systems.

A better understandin of the invention may be had from the fol owing description, when taken in conjunction with the accompanying drawing, which represents the preferred-embodiment of the invention. With Figs. 1 to '6 arranged in the manner shown in Fig.7, a;complete picture transmission system embodying the features of this invention, is disclosed.

Coming now tothe detailed description of the system, as illustrated in Figs. 1' to 6, a transmitting drum 10, upon which-is mounted a transparency of the picture to be transmitted, is rotated and moved axially by a phonic wheel motor 12 which is driven by two pairs of oppositely disposed driving magnets 13. These driving magnets are energized in accordance with the operation of a tuning fork 14.. The drum 10 is mounted on the shaft 11 which is carried by a carriage 15 which slides on guides mounted in a stationary frame 16. The carriage .15 is moved along the frame 16 by the rotation of shaft 17 which is threaded for a part of its length and which engages threads in an upright of the carriage 15. The rotation of shaft 17 causes the corresponding rotation of shaft 11 through gears 19 and 20. Gear 20 rotates with the shaft 17 but also slides along this shaft due to a fixed key 18.

Phonic wheel motor 121 communicates its sitioned by a suitable collar. On one face other.

' rom engaging t of the ar 24 is a toothed wheel or gear 26 which is arran ed to be meshed with a toothed sector 2% which is normally springressed by spri'n 28 but which is prevented g he teeth in the gear 26 due to the position of a stop member 30 engaging arm-29 carrying the toothed sector 27. The stop member 30 is controlled by a release magnet 31. The energization of magnet 31 attracts its armature and removes the stop member 30 from engagement with arm 29, thereby permitting the engagement of the toothed sector 27 with the teeth in the gear 26, and forming a semi-positive clutch between the gear 24 and the shaft 17 to which the member 29 is secured. Power is thus im arted to the shaft 17 for causing the rotation and axial movement of the drum 10. The tuning fork 14 is driven by a magnet 34 by current from a power source, not shown, connected to switch 49. The driving magnet circuit is intermittently interrupted at contact 35. Connected across the magnet 34 is a spark killer resistance 36. The phonic wheel motor 12 is also driven by power from the power source, not shown, through contacts 39 and 40. A resistance 41 is connected in series with the clutch magnet 31 and serves to regulate the current therein. A spark killing circuit consisting of reslstances 42 and 43 and condensers 44 and 45 is associated with contacts 39 and 40 for eliminating the sparking action at these contacts. Contact,

spring 33 carried by the tuning fork 14, but insulated therefrom, and contact 47 are connected through conductors 53 and 54 to the synchronizing carrier wave oscillator shown in Fig. 2.

The energizing circuit of the release magnet 31 extends through the main switch 48, the control switch 49 and the stop switches 50 and 51. When the switch 49 is thrown to the left, art of stop switches 50 and 51 are affected or opening the circuit of the release magnet 31 as well as the driving magnet 34 of the tuning fork 14, for stopping the respective actions. With the switch 49 in. its right hand position, the other half of stop switches 50 and 51 are aifected for performing a similar function when the drum 10 is moving in the opposite direction. In this connection, it should be noted that stop switches 50 and 51 are each provided with a multiplicity of contacts, two arms being provided for each switch, one 'ust ahead of the The two arms 0 each of these switches are provided for the purpose of o nin the circuit of the release magnet 31 w en t e picture 'drum 10 has reached the end of its travel or the transmission of the picture, but to also provide against the possibility of the operator failing to reverse the direction of the motor, thereby driving the motor for moving the drum 10 in the opposite direction. The second set of switchcontacts is provided for opening the circu t of the release ma net 31 and the operating cir- .cuit-of the driving magnet 34 in the event that the carriage moves in the wrong direction. In order to prevent interference from the tuning fork 14, this fork together with the associated spark killers is enclosed in a copper shield 63.

Mounted within the drum 10 is a photoelectric cell' 64. This cell consists of an with the anode 65. A small clear glass window 68 is provided in the cathode to allow the entrance of light from an illuminating source 69. An image of an aperture in the screen 70 which is intensely illuminated by light from source 69 is projected by lens 71 upon the surface of the drum 10 to illuminate an elemental area thereof. The tone value of the elemental area determines the amount of light impressed upon the cathode of the photoelectric cell 64, and in this way the current assing through this photoelectrio cell is etermm'ed b the tone value of the picture to be transmitted.

The electrodes of the photoelectric cell 64 are connected to apicture amplifier PGA, Fig. 2, by conductors 72 and 73 through a double pole double throw switch 100.

The picture current amplifier PGA consists of two electron discharge devices 105 and 106 each of the three element type. The

filaments of the devices 105 and 106 are heated from batteries 107 and 108 respectively, although obviously a common loatput circuit of the electron discharge device 105 through a sourceof potential 103 and a resistance 104. Static polarizing potential for device 105 is supplied through resistance 110' connected in' the filament circuit thereof. The source of potential 103 is divided into three sections 110, 111, and 112. Section '110 is made up of large steps of battery the terminals of which are connected to the switch points of a multi-contact switch 113. Section 111 is made up of smaller gradations of batteries the terminals of which are similarly connected to contact points of a switch 114. Section 112 consists of a potentiometer 115 connected in parallel with battery 112 and a resistance 116 in series for making finer adjustments of the applied transmitted and a positive circuit of the device voltage. Switches 118 and 114 are provided w1th double arms with resistances 117 and- 118, respectively, connected between the switcharms so as to allow the connection of any number of available batteries 1n series without opening the main circuit or short circuiting any of the batteries. Switch is provided to permit a reversal of the connections to the input circuit of picture amplifier PCA so that pictures may be or negative reproduced from a positive.

Connected in the output circuit of the device is a battery 120, resistance 121 and an ammeter 122.- The input circuit of the device 106 is connected to an intermediate point of the battery 120. The grid electrode of the device 106 is given a static biasing potential by means of a potentiometer 123 connected across a battery 124, the circuit of which is controlled by means of a switch 125. Connected in the output circuit of the tube 106 is a battery 127, a resistance 128, and an ammeter 129.

The picture current modulator PM comprises an electron discharge device 131 or the three-element type. The grid electrode of this device is connected with a biasing potential through a potentiometer 132 which is connected across battery 134 through a resistance 133. Switch 135 when thrown to the right closes the potentiometer circuit at contacts 136 and 137 and connects the inputcircuit of the modulator PM to. the output 106 which forms a part of the picture current amplifier PCA. With the switch 135 in the right hand position, the biasing potential is changed to facilitate the adjustment of the current prior to the transmission of the picture. When the switch 135 is thrown to the left, the circuit of the potentiometer 132 is connected in series with the input circuit of the picture modulator PM at contact 139. The picture carrier Wave oscillator circuit is connected to the input circuit of the picture modulator PM through a suitable transformer 140 which has connected across its secondary winding a resistance 141. There is connected in the output circuit of the electron dischargedevice 131 the primary winding of a transformer 143, an ammeter 142 and a battery 144.

Associable with the picture modulator PM is a picture oscillator PO which consists of an electron discharge device of the three-element type. The filament of the device 150 is heated from battery 151 while the plate current for this device is supplied from battery 152 through a suitable choke coil 153. Also connected in the output c1rcuit of the device 150 is a resistance 154 and a potentiometer 155. A feed-back circuit for the device 150 is provided through re sistance 156 and transformer 157. The frenected in t quency of the termined b a condenser 158 which is coniie primary circuit of the transformer 157. A biasing potential for the grid electrode of. the device 150 is supplied from a battery 159 connected to the second ary winding of the transformer 157. Condenser 161 is connected in the output circuit of the device 150 and serves as a blocking condenser to prevent current from battery 152 from affecting transformer 157. Picture oscillator PO is connected to the picture modulator PM through a shielded transformer and the contacts of a switch 163 which may be operated for disconnecting the picture oscillator from the picture modulator and connecting the same directly to contact 201 of key 200. The picture oscillator may be connected either to the picture filter or the test and signal detector depend ing on the position of key 200. Connected in bridge 0 this circuit is a resistance 202 serving to stabilize the action of the cur-' rent on the electron discharge devices.

The synchronizing carrier wave controlling the operation of the tuning fork at the receiving station, is supplied by an oscillator SO which consists of an electron discharge device 170, the filament of which is heated from a battery 171. Plate current for the device is supplied from a battery 172 through a suitable choke-coil 173. The generated wave is supplied to a modulator circuit 174 through a resistance 175 and a transformer 176. As described in connection With the picture oscillator PO, a similar feed-back circuit is provided for the electron dischar e device 170 consistin r of a resist ance 17% and a transformer 148. The frequency of the generated wave is similarly controlled by means of a condenser 179 connected in the primary circuit of the transformer 178. In order to prevent current from the battery 172 reaching the transformer 178, a stopping condenser 181 is connected in the output circuit of the device 170. The synchronizing carrier wave transmitted to the line is controlled by contact 33 of the tuning fork 14 through conductors 53 and 54, and in this way the frequency of interruption of the synchronizing carrier wave is determined by the operation of the tuning fork 14 which serves as a pace setting device for the transmission of the synchronizing carrier wave.

The secondary winding of the transformer 143 is connected to the picture channel filter 166 through switch 163 and contacts of a multi-contact key 200 and from thence the signals are transmitted through a suitable amplifier to the line. The output circuit of the synchronizing oscillator S0 is connected to a control channel filter 183 which is connected in parallel with the output circuit of the picture channel filter 166. From this generated carrier wave is deloo - 'point, the picture carrier wave and the synchronizing carrier wave appear in the same circuit and are simultaneously impressed on the amplifier TA.

Referring now to Fig. 3, the amplifier TA and the test. and signal detector 218 and- The secondary winding of the transformer 212 is connected through normally closed contacts of switches 230, 232, 233 and 234 to the primary winding of a transformer 243,

.the secondary winding of which is connected to the line conductors 322 and 323 extending to the distant station where picture receiving and reproducing apparatus is located.

The test and si al detector 218 comprises two three-electro e electron discharge devices 220 and 221 with their associated circuits. The device 220 is connected to contacts-of key 200 through a suitable transformer 219. Similarly, the output circuit of the device 220 is connected with the input, circuit of the device 221 through a transformer. Connected in the output circuit of the device 221 is a condenser 222 and an ammeter 223 with associated resistance. Connected in a circuit common to the output circuit of the device 221 is a relay 246 and a resistance 247. Relay 246 controls a buzzer 248. The buzzer 248 is operated only upon the receipt from the distant station of a predetermined current frequency for apprising the operator at the sending station that the distant operator desires to communicate with him telephonically and serves by means of code signals to convey certain information to the transmitting operator. It is thus seen that the test and signal detector 218 functions as a detector of signals received from the distant station for causing predetermined operations. It is also made use of for test purposes, being connected to the contacts of key 200 which. when in its actuated position, connects the potentiometers 213 and 214 through resistance pads 215, 216 and 217 .With the output circuit of the picture modulator PM. The resistances 215, 216 and 217 simulate the impedance of the picture filter, thus facilitating the test operations. The potentiometer 214 is for the purpose of adjusting the carrier current wave for the light and dark conditions. In other Words, this potentiometer determines the contrast between the light and dark shades of the picthereby reducing the loss introduced by po-' tentiometer 214 by an amount equal to the desired contrast. A clear film is also substituted for the opaque screen. The photo-electric cell battery sections 110, 111 and 112 are then adjusted to roduce the same reading, as before, of t e ammeter 223. In this way, adjustments may be made to vary the contrast between the light and dark portions of the picture.

To test the picture oscillator switch 163 and key 200 are operated to connect the entire secondary winding of transformer 160 with the test and signal detector 218. By watching the ammeter 223, the reading of which may be controlled by potentiometer 213, the variationsin the amount of current generated by the picture oscillator may be determined.

When it is desired to make line tests switch'230 may be operated to terminate the line in a predetermined impedance. Key 230 opens at its inner contacts the secondar circult of the transformer 212 of the amphfier TA and closes at its outer contacts a circuit, including the resistance 231, the impedance of which is selected so as to be substantially of the same value as the impedance of the line when associated with the connecting circuits. With the resistance 231 substituted for the amplifier TA, various tests may be made from the receiving station or any other point along the line to determine theoperating conditions of the line.

Key 233 serves to disconnect the apparatus and circuits to the right thereof and connects test or meter panel 236 to the output circuit of the amplifier TA. The test or meter panel 236 comprises a pair of thermocouples 237 and 238 which are connected to an ammeter 239. The effectiveness of the thermocouples is controlled by means of a key 240 which inserts a resistance 253 in circuit with the heating element of thermocouple 237.. Thermocouple 237 is connected to ammeter 239 when key 240 is operated in either direction. When it is desired to connect the ammeter 239 to thermocouple 238, switch 242 is operated. \Vith the thermocouple connected to the output circuit of the amplifier TA through key 233, various tests may be made to determine the transmission efficiency of the system. It may also be desired to connect the test or meter panel 236 with various other parts of the system. In order to permit the association of the test or meter panel 236 with various parts of the system. the elements of the thermocouples terminate in contacts of jacks 241 and 244 which, by means of plugs and cords, may be extended to any'dcsircd point.

For the piirpose of making tests on the stability of the system key 234 is arranged for disconnecting the primary winding of the transformer 243 and connecting the part of the system to the left of this point with the test and signal detector 218 through the normally closed contacts of key 200. With these connections complete. the system may be tested up to the point of the transmission of the carrier current waves to the transformer 243. It should also be noted that, upon the operation of key 234, the circuit for buzzer 248 through the contacts of relay 246 is opened at the lower contact of this key, thereby preventing the operation of the interrupter in the event that relay 246 operates.

Key 232. when operated. disconnects the amplifier TA from the line and connects thereto inductances 249 which are included in a circuit extending to the contacts of a key 251 which functions to connect a telephone set 250 therewith. When keys 232 and 251 are actuated, telephone communication may be carried on between the connected stations over the same circuit as that utilized for transmitting the picture carrier wave. I

The amplified current from the amplifier TA passes through the transformer 243 over the line conductors 322 and 323 to the receiving or reproducing station where the line conductors terminate in the primary w1nding of a transformer 300. According to the preferred form of the invention, the secondary winding of the transformer 300 1s connected as a hybrid coil for permitting the transmission of currents in both directions. Connected with the mid-tap of the secondary winding of the transformer 300 IS an adjustable resistance 301 and an ad ustable condenser 302. These units are adgusted to balance the line so that incoming and outgoing currents divide properly between the various branches. One of the outside terminals of the secondary winding of transformer 300, the common branch of the resistance 301 and condenser 302oppos1te the connection to the transformer 300, are connected through the inner contacts of a key 315 to the input circuit of a rece ving amplifier RA. This amplifier consists of a three-element electron discharge device 318 which has its input circuit connected to the circuit extending from the secondary winding of the transformer 300 by means of a transformer 319. Connected in the primary circuit of the transformer 319 is a potentiometer 320 for adjusting the current impressed on the input circuit of the electron discharge device 318.

For the purpose of apprising the operator at the distant transmitting station that the operator at the receiving station desires to communicate with him telephonically or to conve other information by means of code slgna s as previously agreed to, a key 303 for associating an interrupter 304 through a slgnal filter 305 is provided. The interru tor 304 has been shown diagrammati'cal y, since the interrupter per se does not form a part of the present invention, for obviously any one of several types of interrupters could be used with equally good results. When the key 303 is actuated, the interrupter 304.is set in operation due to the connection of a battery through contact 306 therewith for transmitting through the signal filter 305, contact 308 of the key 303 over the line conductors 322 and 323 to the distant transmitting station, a current wave which is allowed to pass only through the signal filter 204, from whence 1t is impressed on the input circuit of the test and signal detector 218 Where it is effective to cause the operation of relay 246 and the operation of buzzer 248. It should be noted that signaling between the two stations may be accomplished at any time during the operation of the system, that is, during the transmission of pictures. L1 other words, the present form of signaling may be utilized for interrupting the transmission of the picture should the receiving operator detect some fault or irregularity in the transmission of the picture without permitting its complete transmission and then informing the transmitting operator of the difficulties encountered. A key 315 is provided for connecting a telephone 316 with the line conductors 322 and 323 through the transformer 300, at the same time disconnecting the receiving amplifier RA.

The output circuit of the electron discharge device 318 is connected with a common circuit including filters 400 and 401 by means of a transformer 321. Filters 400 and 401 are similar to filters 166 and 183. The respective filters pass only the designated carrier current waves. In other words, filter 400 passes the carrier current wave modulated in accordance with the picture, while filter 401 allows only the synchronizing carrier Wave to pass.

The carrier current wave passed by filter 400 is impressed on the input circuit of a receiver picture amplifier RPA which consists of an electron discharge device 403. The electron discharge device 403 is connected with the filter 400 through a transformer 405, the primary circuit of which has connected therein a potentiometer 404. The amplified earner wave is either amplified or detected v in a receiving detector amplifier RDA accordingly as to whether it is required to control the o eration of a light valve or the starting 0 the receiving picture drum.

The reproducing amplifier detector RDA consisting of an electron discharge device 410 has its input circuit connected with the output circuit of"the device 403 through a transformer 411. The filaments of the electron discharge'device 403 and 410 are heated by current from a battery 406 through an adjustable resistance 407. Corresponding changes in the bias of these two electron discharge devices may therefore be made through a single adjustment which has been found to improve the operation of the system. A static polarizing potential for the electron discharge device 403 is furnished from aresistance 408-in series with the filament of device 403.

For picture reproduction, the reproducing picture amplifier RDA functions as an amplifier, while for starting 'or releasing the re producing mechanism, it functions as a detector. When device 410 is functioning as an amplifier, the grid electrode thereof is polarized by battery 416, the circuit of which is closed through contact 419 of relay 415-. When functioning as a detector, the grid is maintained at a larger negative potential by battery 418 which is connected into the grid circuit upon the operation of relay 415 through contact 424. A by-pass condenser 425 is connected in the plate circuit of the device 410 upon the operation of relay 415, thereby providing a low impedance path for the picture carrier wave. The plate electrode of the device 410 is connected to the primary winding of the transformer 422 through the normally closed contact 423 of relay 415.

If relay 415 is energized either by the closure of switch 313 or the closure of the left hand contact of relay 501, battery 418 is substituted for battery 416 thereby sufiiciently biasing the device 410 for effecting its operation as a detector. If the carrier wave is incoming from the distant station, detected current in the output circuit of the receiving detector amplifier RDA will cause the operation of relay 501. This relay has three windings, the middle one being connected to the primary winding of a trans: former 505 which has one terminal connected directly to the right hand 'front contact of relay 415, while the other terminal is connected to the middle winding of this relay. The-lower winding has included in its circuit the secondary winding of thetransformer 505. Thus, when a carrier wave is detected by the electron discharge device 410, an impulse passes through the primary winding of transformer 505 and the middle Winding of relay 501. Simultaneously therewith, a current is induced into the secthe contacts of this relay.

ondary .winding of the transformer 505:- which acts on the lower Winding of the relay to accelerate the movement of the relay armature to its other contact. It should be noted also that the upper windin of the relay 501 serves as a biasing winding for returnin the relay armature to its other position. iasing current for this relay is supplied by battery 406 through adjustable resistance 407. It will be remembered that battery 406 also furnished the heatin cur rent-for-the filaments of electron disc large devices 403 and 410. By having the heating current for the devices 403 and 410 and the biasing current for relay 501 supplied from a common battery through an adjustable resistance, the same bias may be applied to the respective devices, thereby simplifying the operation of the apparatus. The contacts of the relay 501 are bridged by resistances 502 and 506 and condensers 503 and- 504 for eliminating the sparking action at There is also connccted in circuit with the middle winding of this relay an ammeter 507 servin'g'to indicate the current passing through this part of the circuit.

The synchronizing current wave passed by the filter 401 is amplified in reproducin synchronizing amplifier BSA and detects in reproducing synchronizing detector BSD. The amplifier consists of an electron discharge device 430 which is coupled with the filter 401 by means of a transformer 431. As in the case of the electron discharge de- 100 vice 403, a potentiometer 432 is connected in the primary circuit of the transformer 431 for controlling the current applied thereto. The output circuit of the electron discharge device 430 is connected by means 105 of a transformer 433 to the input circuit of an electron discharge device 434 forming a part of the reproducing synchronizing detector BSD.. Static biasing potential for device 430 is supplied by a resistance connectmy ed in the filament circuit. The output cir cuit of the device 434 includes a by-pass condenser 435 and a resistance 436 which is connected to the upper winding of relay 508. Like relay 501, one winding of relay 115 508 is controlled by current induced inthe secondary winding of a transformer 509, the primary circuit of which is connected with the resistance 436 and in turn the output circuit of the device 434. Biasing cur- 12o rent for the relay 508 is supplied in a manner similar to that described for the electron discharge devices 403 and 410. Bridged acrossthe contacts of relay 508 are resistances-510 and 511 and condensers 512 12 and 513 for eliminating sparkin An ammeter 514 is connected in circuit with the winding of relay 508 for ascertaining the current flowing through the connected wind- Relay 508 controls throu h its contacts the operation of a tuning ork 523 which controls the rotation of a phonic wheel motor 533. There is also connected with the left hand contact of relay 508 the winding of relay 516 which controls through its contacts the operation of a buzzer 517. Relay 516 is slow releasing and is normally energized and therefore buzzer 517 is normally quiet, but should relay '508 be operated to engage its left hand contact for an appreciable period of time, the winding of relay 516 is short circuited causing the release of this relay and the operation of the buzzer517 which communicates certain information to the receiving operator from the transmitting operator, as will later be more fully described.

With switch 526 engaging its upper contact, a circuit is completed between the contacts of relay 508 and the winding of electromagnet 522 which drives the tuning fork 523.

The tuning fork 523 may also be driven independently of the contacts of relay 508 by closing switch 526 in its lower position so that the energizing circuit of magnet 522 errtends through contact 527. The phonic wheel motor 533 is driven through the action of diametrically disposed magnets 534 which are connected to contacts 553 and 554 controlled by the tuning fork 523. Connected with the contacts 553 and 554 are resistances 528 and 529 and condensers 530 and 531, serving to reduce the sparking action at the connected contacts.

The phonic Wheel motor 533 has its shaft connected through a worm gear 535 to a gear wheel 536 rotatably mounted on a shaft 537. Power from the gear 536 is imparted to shaft 537 which is threaded for a portion of its length and which has slidably mounted thereon a gear 540 through a clutch mechan sm consisting of a toothed wheel 544 and a toothed sector 545. The former is connected to gear 536 While the latter is fixed to the shaft 537 and is normally spring-pressed, but is prevented from engaging wheel 544 due to a stop546. The stop 546 is controlled by a release magnet 547 which in turn is controlled by relay 501 through the contacts of switch 548 and stop switches 549 and 550. The shaft 537 is fitted in a carriage 543 which slides in guides formed in a stationary carriage 538. The gear 540 is meshed with the teeth of a gear 541 which is secured to a shaft 542 on which the reproducing drum 544 is secured. Stop switches 549 and 550 serve the same purpose as similar switches described in connection with the transmitting mechan sm.

The output circuit of the receiving detector amplifier RDA is connected with a light valve 557 through a transformer 422 which has its secondary winding connected to the 1 1t valve 557 comprises a single strin 558 w llCh is'suspended in a niagnetic fie d of maintained by current in constant strength winding 559. The strin amount of light impresse tive surface 556 secured from a light source 560 through suitable lenses 561 and 562. For further details of the operation and construction of the light valve, reference should be had to a copending application of H. E. Ives, Serial No. 711,7 55, filed May 8, 1924.

A description of the transmission of a picture and the operations incident thereto will now be given. With key 48, Fig. 1, in its normal position, the circuit for clutch magnet 31 is open, thereby preventing the energization of this magnet even should key 49 be closed. However, with the key 48 act-uated, a circuit for theclutch magnet 31 is extended to the contacts of start key 49. By the closure of key 313, Fig. 4, relay 415 is energized to convert the reproducing detector amplifier RDA from an amplifier to a detector. lVhen this relay operates, a resistance 420, which is normally in bridge of'the primary circuit of transformer 405, is disconnected while the serial resistance 421 is short circuited, thus facilitating the operation of the discharge devices 403 and 410. The detected incoming carrier wave then energizes relay 501 to maintain relay 415 energized independently of key 313.- The energization of relay 501 opens the circuit of clutch magnet 547 at its right hand contact, thereby preventing the energization of this magnet. lVith switch 49 thrown to its left hand position and key 52 actuated, clutch magnet 31 is energized over a circuit including the contacts of key 49 and the contacts of stop switches 50 and 51. The energization of clutch magnet 31 withdraws the stop 30 from engagement with the arm 29, allowing the toothed sector 27 to engage the gear wheel 26, thereby causing the rotation of drum 10 upon which is mounted a transparency of the picture to be transmitted.

The carrier Wave from the oscillator PO is interrupted due to the closure of the right hand contact of key 52. The interruption of the carrier wave causes the deenergization of relay 501 to engage its right hand contact. With the switch 548 in its left hand position, a circuit is completed including the winding of clutch magnet 547 with the terminals of an operating battery. The deenergization of relay 501 also opens the holding circuit for relay 415 causing the deenergization of this relay and the conversion of the receiving detector amplifier RDA to an amplifier. With switch 52 in its normal position, the carrier wave from oscillator PO is impressed upon the modulator PM through the transformer 140. The output circuit of the modulator is 558 controls the on a photo-sensito the drum 544 connected by means of a transformer 143 to 'the picture channel filter 166, and thence by exposure of the photo-sensitive surface 556.

In order to permit the receiving operator to signal and connnunicate with the transmitting operator over the same circuit as the modulated picture carrier waves are transmitted, the interrupter 304 is arranged to be connected with the line conductors 322 and 323 upon the actuation of key 303. The current wave impressed on the conductors 322 and 323 through transformer 300 is received at the transmitting station and passed through transformer 243. The characteristic of the signal filter 204 is such that it passes only the carrier wave generated by the interrupter 304. The carrier wave passed by the filter 204 is impressed through the potentiometer 245 and the upper and lower contacts of key 234 and the contacts of key 200 on the test and signal detector 218. The impressed carrier wave is detected. and impressed on relay 246 causing the energization of this relay. Relay 246 in operating energizes relay 248 which acts as a buzzer and which gives an audible signal to the transmitting operator. The transmitting operator maythen communicate with the receiving operator telephonically by actuating keys 232 and 251 provided thereceiving operator has actuated a similar key 315. Each of these keys connects a telephone set with the connecting circuit after which the operators may communicate with each other. The circuits are so arranged that it is not necessary for the receiving operator to await the completion of the transmission of the picture before signaling the transmitting operator. In other words, the receiving operator maye-fl'ect the operation of the-buzzer 248 during the transmission of the picture or at any other time.

The transmitting operator may also desire to signal the receiving operator. This particular feature is accomplished through the location of a key 252 in circuit with the output circuit of the synchronizing oscillator SO. When this key is operated, the modulating circuit through the tuning fork contacts 33 and 47 is interrupted, transmitting a continuous carrier wave thereby causing relay 508 to operate to its left hand'contact for a time dependent upon the time during which key 252 is -actuated for short circuiting the winding of relay 516. Relay 516 releases its armature, closing the circuit for buzzer 517. Buzzer 517 gives an audible signal to the receiving operator who may i then actuate key 315 for associating telephone set 316 with the line conductors 322 and 323. The transmitting operator'may, by operating keys 232 and 251, now communicate telephonically with the receiving operator over the same circuit'as that over which the modulated picture carrier wave and the synchronizing carrier wave are transmitted.

The method of operation will now be described. The picture. drums 10 and 544 at the transmitting and receiving stations re-- spectively are set at starting position in any suitable manner which, under ordinary conditions, will be in this position. The transparency of the picture to be transmitted is secured to the drum 10, while the photo-sensitive surface or film 556 is mounted on the drum 544. Switch 48 being closed, key 49 is actuated to the left, whereby the energizing circuit for the release magnet 31 .ergization of clutch magnet 547.

Synchronizing carrier waves from the oscillator SO in accordance with the vibration ,of tuning fork 14 are transmitted through modulator circuit 174, control channel filter 183, amplifier TA, transformer 243, the line conductors 322 and 323 to the reproducing or receiving station, fromv whence they pass through transformer 300, the filter 401 and are im ressed on the receiving synchronizing amp ifier and receiving synchronizing detector RSA and RSD. Picture carrier wave is supplied by oscillator PO to modulator PM by way and transmitted through filter 166, amplifier TA and transformer 243 to line conductors 322 and 323. The carrier wave received at the reproducing or receiving station passes through the receiving amplifier RA and the filter 400 and impressed on the reproducing picture amplifier and reproducmg picture detector EPA, and RDA before being impressed on the light valve 557.

With the picture carrier wave impressed on the line at the transmitting station, key 313 is actuated long enough to permit the energization and locking up of relay 415 which converts the amplifier RDA tov a detector. This relay is now held energized over a circuit including the contacts of relay 501. Switch 548 is then moved to its left hand position which prepares a circuit for the clutch magnet 547 which is later to be completed through the contacts of relay 501.

Tuning'fork 523 is then set in vibrationof transformer 140. Y

the left hand contacts of the switch 549 will be opened, thereby opening the holding circuit for the clutch magnet 547.

The circuit of the oscillator SO is intermittently interrupted at contacts 33 and 47 of tuning fork 14, thus transmitting to line periodic impulses in accordance with the viration of the tuning fork 14.. The receipt left hand contact the circuit .prepared forclutch magnet 31, causing the energization and locking up of this magnet. This key also closes at its right hand contact a short circuit for the modulator PM, thereby interrupting the carrier wave transmitted to the reproducing terminal. The interruption of the carrier wave causes the deenergization of relay 501 at the receiving station due to the detector action of receiving detector amplifier RDA and in consequence ,the energization of clutch magnet 547. .The clutch'magnets 31 and 547 associated with the transmitting and receiving picture drums respectively cause these drums to be released simultaneously. Relay 501 in deenergizing o ens at its contacts the holding circuit for re ay 415 releasing this relay, and converting the receiving detector amplifier RDA from a detector to an amplifier.

The elemental areas of the picture of the transparency which is secured tothe drum 10, are successively brought into alignment with the light source 69 and the photoelectrio cell 64. Consequently, picture currents are impressed on the picture current amplifier and picture current modulater PM, to the line conductors 322 and 323, thence to the receiving amplifier RA, filter 400, receiving picture amplifier RPA, receiving detector amplifier RDA to the light valve 557. The light valve 557 is thus actuated in accordance with the received carrier wave for controlling the exposure of light sensitive surface 556 mounted on the drum 544.

As the carriage 15 moves to the right, it encounters stop switch 51 opening at its contacts the holding circuit for the clutch magnet 31 and the operating circuit of the driving magnet 34 of tuning fork 14. Stop member 30 is then positioned in the path of the stop arm 29 causing the stop age of the shaft 18 and in consequence the rum 10 upon its engagement therewith. The tuning fork 14 is also arrested. At the reproducing terminal, the carriage 543 en ages the first switch member of stop switc 550 opening the energizing circuit of clutch magnet 547, and accordingly the stoppage of the drum 544. The light sensitive surface 556, having been exposed in accordance with the operation of the light valve 557 which responded to the carrier wave impressed thereon, may now be removed from the drum 544 and developed in the usual method employed in photogra hy.

The invention has been described with reference to a particular t pe of system, although obviously it may he applied to other systems for the transmission of pictures b e ectricity without departing from the spirit and scope of the present invention. It isv therefore not intended that the invention should be limited to the particular system chosen for illustration but onlyby the appended claims.

- What is claimed is:

1. In a picture transmitting system, a transmltting and a reproducing station, a signaling clrcuit connecting said stations, means at the transmitting station for transmltting over said circuit current waves in accordance with the elemental tone values of the picture, means at the reproducing station responsive to said current waves for controlling the reproduction of the picture, means for generating a synchronizing wave to effect the synchronous movement of the means at the transmitting and reproducing stations, a signaling device at the reproducing station, and means at the transmitting station for changing said synchronizin wave to cause the operation of said signa mg device.

2. In a picture transmitting system, a transmitting and a reproducing station, a" signaling circuit connecting said stations, means at the transmitting station for transmitting over said circuit current waves in accordance with the elemental tone values of the picture, means at the reproducing station responsive to said current waves for controlling the reproduction of the picture, means for generating an interrupted synchronizin wave to eflect a synchronous movement 0 the means at the transmitting and reproducing stations, means at the reproducing station responsive to said synchronizing wave to eflect the synchronousoperation of the reproducing means, a signaling device controlled thereby, and means at the transmitting station for increasin the time between interruptions of the sync ronizing wave to cause a prolonged energization of said means and accordingly the operation of said signaling device.

3. In a picture transmitting system, a transmitting and a reproducing station, a signaling circuit connecting sai stations, means at the transmitting station for transmitting over said circuit current waves in accordance with the elemental tone values of the picture, means at the reproducing station responsive to said current waves for controlling the reproduction of the picture, means for generating an interrupted synchronizing wave to effect a synchronous movement of the means at the'transmitting and reproducing stations,'a relay atthe reproducing station res onsive to said synchronizing wave to effect tlie synchronous operation of the reproducing means, a signaling device controlled thereby, and means at the transmitting station for increasing the time between interruptions of the synchronizing wave to cause said relay to hold over for an appreciable period of time to operate said signaling device.

4. In a picture transmission system, a transmittin and a reproducing station, a signaling circuit connected to said stations, means at the transmitting station for transmitting over said circuit a current wave modulated in accordance with the elemental tone values of the picture, means at the receivin station responsive to said current wave or controlling the reproduction of the picture, means at the receiving station for impressing on said circuit a current of a predetermined frequency, means at said transmitting station responsive only to said current of a predetermined frequency, and means operated by said last recited means for signaling the transmitting operator.

5. In a picture transmission system a transmitting and a reproducing station, a

signaling circuit connected to said stations, means at the transmittin station for transmitting over said circuit a current wave modulated in accordance with the elemental tone values of the picture, means at the receiving station responsive to said current wave or reproducing the picture, means at the receiving station for impressing on said circuit a current of a predetermined frequency, a signal filter associated with said circuit effective to allow said current of predetermined frequency to pass, an electron discharge device operated by the current passed by said filter, and a signaling device associated with said electron discharge device and operated by the detected current for signaling the transmitting operator.

6. In a picture transmitting system, a transmitting and a reproducing station, a signaling circuit connecting said stations, means at the transmitting station for transmitting over said circuit current waves in accordance with the elemental tone values of the picture, means at the reproducing station responsive to said current waves for controlling the reproduction of the picture, means for generating a synchronizing wave to effect the synchronous movement of the means at said stations, a signaling device at the reproducing station, means at the transmitting station for changing said synchronizin wave to cause the operation of said signa ing device, means at the reproducing station for impressing on said circuit a current wave of a frequency different from the current wave transmitted from the transmitting station, and means at the transmitting station controlled by said current wave impressed at the reproducing station.

In witness whereof, we hereunto subscribe our names this 30th day of December, A. D. 1924:.

ERWIN P. BANCROFT. JOHN C. BURKHOLDER, JR. WALTER A. PHELPS. 

